iStockPhoto/Thinkstock(NEW YORK) -- Beyond leaving you drowsy and irritable, sleepless nights can take a serious toll on your physical and mental health.

"We know sleep is a critical biological function that influences a wide variety of physiological process," said Dr. Susan Redline, a sleep specialist at Brigham and Women's Hospital in Boston. "Sleep deficiency can affect mood and the ability to make memories and learn, but it also affects metabolism, appetite, blood pressure, levels of inflammation in the body and perhaps even the immune response."

Lack of sleep has been linked to stroke, obesity, diabetes, anxiety, depression and the country's number one killers: heart disease and cancer. Read on to learn the health hazards of sleep deficiency and how you can sleep better.

Heart Disease

Getting seven hours of shut-eye after a day of healthy eating and moderate exercise can lower the risk of heart disease by up to 65 percent, according to a 2013 study published in the European Journal of Preventive Cardiology.

"It is always important to confirm results," study author Monique Verschuren of the National Institute for Public Health and the Environment in the Netherlands said in a statement. "But the evidence is certainly growing that sleep should be added to our list of [cardiovascular disease] risk factors."

The study added to a growing body of evidence that sleep is key for heart health. A 2011 study published in the European Heart Journal found people who slept fewer than six hours a night were 48 percent more likely to develop or die from heart disease.

Stroke

A study of more than 5,600 people found those who slept fewer than six hours a night were more likely to suffer a stroke than their well-rested counterparts.

"We speculate that short sleep duration is a precursor to other traditional stroke risk factors, and once these traditional stroke risk factors are present, then perhaps they become stronger risk factors than sleep duration alone," Megan Ruiter of the University of Alabama at Birmingham said in a statement.

Stroke risk is also higher in people who are overweight, diabetic or hypertensive -- all conditions linked to poor sleep.

Obesity and Diabetes

Sporadic and irregular sleep can raise blood sugar levels and slow the body's metabolism, increasing the risk of obesity and diabetes, according to an April 2012 study published in the journal Science Translational Medicine.

"The evidence is clear that getting enough sleep is important for health," said study author Orfeu Buxton, a neuroscientist at Brigham and Women's Hospital in Boston.

Sleep deficiency can also lead to bad food choices, according to a study that found the sight of unhealthy food activated reward centers in the brains of sleep-deprived people.

"The results suggest that, under restricted sleep, individuals will find unhealthy foods highly salient and rewarding, which may lead to greater consumption of those foods," said study author Marie-Pierre St-Onge from St. Luke's Roosevelt Hospital Center and Columbia University in New York. "Indeed, food intake data from this same study showed that participants ate more overall and consumed more fat after a period of sleep restriction compared to regular sleep."

Anxiety and Depression

Sure, sleepless nights make for miserable mornings. But chronic sleep deficiency can lead to anxiety and depression -- both serious mood disorders.

"People feel more anxious, restless, irritable, less satisfied," said Dr. Mark Dyken, director of the University of Iowa's Sleep Disorders Center in Iowa City, Iowa, adding sleep deficiency can impact careers and relationships. "They have difficulty focusing and sometimes feel like they just don't care anymore."

Brain imaging suggests sleep deprivation can boost activity in the brain's emotional centers, according to a study presented at the Associated Professional Sleep Societies in Boston.

"Our results suggest that just one night of sleep loss significantly alters the optimal functioning of this essential brain process, especially among anxious individuals," study author Andrea Goldstein from the Sleep and Neuroimaging Laboratory at the University of California, Berkeley, said in a statement. "This is perhaps never more relevant considering the continued erosion of sleep time that continues to occur across society."

Cancer

Sleep deficiency has also been linked to an increased risk of cancer.

A 2008 study published in the British Journal of Cancer found women who slept fewer than six hours a night were more likely develop breast cancer, and a 2010 study published in the journal Cancer found those who slept fewer than six hours a night were more likely to have colorectal polyps, which can lead to colon cancer.

The biological mechanisms are unclear, but lack of sleep has been shown to boost levels of inflammation in the body and interfere with the immune response, both of which have been implicated in cancer.

"Sleep is restorative," said Dyken. "And if you don't get it, your health will suffer."

Dry, Damaged Skin

Dark circles and puffy eyes can make you look tired, but new research suggests lack of sleep can take a serious toll on your skin, causing it to lose moisture and recover more slowly from sun damage.

"When our skin gets dehydrated we're more prone to eczema and other skin conditions," said Dr. Elma Baron, director of UH Case Medical Center's Skin Study Center in Cleveland, who led the study of 60 women sponsored by Estee Lauder. "Good sleepers have better skin barrier function, and poor sleepers lose more moisture through the skin."

Sleep quality and duration also seemed to impact skin's pigmentation and laxity, according to Baron, and good sleepers tended to feel better about the way they looked.

"I think it emphasizes the importance of good quality sleep and adequate sleep," said Baron.

The study was presented at the International Investigative Dermatology Meeting in Edinburgh, Scotland, and is currently being prepared for publication, according to Baron.

Get Your Sleep

With hectic work and family schedules, getting a good night's sleep is no easy feat. But experts say a little planning can go a long way, helping you feel refreshed the next morning and for many to come.

"Make sure your bedroom is dark and quiet, and avoid reading anything that's going to make you excited or worried," said Dyken. "Try not to exercise or eat a big meal within three hours of your bedtime, but don't go to bed hungry, either."

Caffeine and alcohol can also interfere with sleep, according to Redline.

"Much of sleep deficiency is self-inflicted," she said. "But adults should do their best to get to bed at regular times and aim to have seven-and-a-half hours on average of sleep. Set your schedule such that you honor and respect your sleep needs.